Dany's involvement in Meereen is the result of a kind of awkward series of revisions to the original plan for the series. As the first book in the trilogy (A Game of Thrones
) expanded into two and then three books (A Game of Thrones
, A Clash of Kings
, A Storm of Swords
), he devised the idea of a five-year gap to allow certain characters to age, etc. Ruling Meereen was Dany's holding position for the gap, and the fourth book would open with a recounting of what had happened there. But Martin (correctly, I think) decided that the five-year gap really didn't work for a number of stories, so it was junked.